1. Field of the Invention
The present invention relates to a non-contact type tonometer for measuring intraocular pressure of an examinee""s eye by detecting a deformed state of a cornea of the eye caused by a blow of a compressed air (fluid) thereto.
2. Description of Related Art
There has conventionally been known a non-contact type tonometer used for measuring the intraocular pressure of an eye of an examinee by detecting a deformed state of a cornea of the eye caused by an air blow from an air blowing device. A corneal deformation detecting system of this tonometer is constructed of a projection optical system for projecting light to the cornea and a detecting optical system including a photodetector (photosensor) for detecting the amount of light reflected from the cornea. By detecting that the amount of the corneal reflection light detected by the photodetector became the maximum, a deformed state of the cornea is detected.
In the conventional tonometer, however, even when driving of the air blowing device is stopped after detection that the cornea has been deformed into a predetermined state, the air blow is not stopped immediately, thus allowing superfluous air to be blown to the eye. If the examinee blinks his/her eye to be examined, the amount of the corneal reflection light detected by the photodetector of the corneal deformation detecting system does not produce any peak. As a result, the air would be blown at the predetermined maximum pressure against the examinee""s eye. This results in a burden to the examinee""s eye.
The present invention has been made in view of the above circumstances and has an object to overcome the above problems and to provide a non-contact type tonometer capable of reducing a burden to an examinee""s eye.
Additional objects and advantages of the invention will be set forth in part in the description which follows and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the purpose of the invention, there is provided A non-contact type tonometer including: a compressed air blowing unit which compresses air in a cylinder by means of a piston disposed within the cylinder and blows the compressed air to a cornea of an examinee""s eye; a driving unit which drives the piston; a pressure sensor which detects pressure of the air in the cylinder; an optical system which projects light to the cornea; a photosensor which detects, of the light projected by the optical system, reflection light reflected from the cornea; and a controller which obtains a change in pressure for a predetermined time based on a detection result by the pressure sensor when the photosensor detects a predetermined change amount of the reflection light after the driving unit drives the piston to start blowing of the compressed air to the cornea from the compressed air blowing unit, and changes a timing of stopping supply of driving power to the driving unit based on the obtained change in pressure.
According to another aspect of the present invention, there is provided a non-contact type tonometer including: a compressed air blowing unit which compresses air in a cylinder by means of a piston disposed within the cylinder and blows the compressed air to a cornea of an examinee""s eye; a driving unit which drives the piston; a pressure sensor which detects pressure of the air in the cylinder; an optical system which projects light to the cornea; a one-dimensional position detecting element which detects reflection light corresponding to a working distance to the cornea based on the light projected by the optical system and then reflected from the cornea; and a controller which obtains a change in pressure for a predetermined time based on a detection result by the pressure sensor when the one-dimensional position detecting element detects a predetermined change amount of the reflection light after the driving unit drives the piston to start blowing of the compressed air to the cornea from the compressed air blowing unit, and changes a timing of stopping supply of driving power to the driving unit based on the obtained change in pressure.
According to the third aspect of the present invention, there is provided a non-contact type tonometer including: a compressed air blowing unit which compresses air in a cylinder by means of a piston disposed within the cylinder and blows the compressed air to a cornea of an examinee""s eye; a driving unit which drives the piston; a pressure sensor which detects pressure of the air in the cylinder; an optical system which projects light to the cornea; a photosensor which detects, of the light projected by the optical system, reflection light reflected from the cornea; and a controller which obtains a pressure change ratio expressed in a pressure change amount with respect to a predetermined time just before a predetermined change amount of the reflection light is detected by the photosensor after the driving unit drives the piston to start blowing of the compressed air to the cornea from the compressed air blowing unit, and sets the pressure change amount to a small value when the obtained pressure change ratio is large and, alternatively, to a large value when the obtained pressure change ratio is small, and stops supply of driving power to the driving unit based on the set pressure change amount.
According to the fourth aspect of the present invention, there is provided a non-contact type tonometer including: a compressed air blowing unit which compresses air in a cylinder by means of a piston disposed within the cylinder and blows the compressed air to a cornea of an examinee""s eye; a driving unit which drives the piston; an optical system which projects light to the cornea; a photosensor which detects, of the light projected by the optical system, reflection light reflected from the cornea; and a controller which judges that a blink of the examinee""s eye has occurred when a change amount of the reflection light detected by the photosensor decreases by a predetermined amount after the driving unit drives the piston to start blowing of the compressed air to the cornea from the compressed air blowing unit, and stops supply of driving power to the driving unit.